Field of the Invention
Embodiments of the invention relate to a touch sensing system and a method of reducing latency thereof.
Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been indispensably used in portable information appliances and has been expanded to the use of home appliances. A capacitive touch sensing system includes a capacitive touch screen, which has durability and definition better than an existing resistive touch screen and is able to recognize a multi-touch input and a proximity touch input, thereby making it possible to be applied to various applications. In the touch sensing system, a touch report rate has to increase so as to increase the touch sensitivity a user feels and accurately recognize a touch input trace or a dragging trace. The touch report rate is a velocity or a frequency (Hz), at which coordinate information of touch data obtained by sensing touch sensors present in the touch screen is transmitted to an external host system.
In general, the touch sensing system supplies driving signals to the touch sensors through lines formed on the touch screen, senses a change in voltages of the touch sensors before and after a touch operation, and converts a change amount of the voltage into digital data, i.e., touch raw data. The touch sensing system compares the touch raw data with a predetermined threshold value. The touch sensing system decides touch raw data, which is greater than the threshold value, as touch data obtained from the touch sensor, in which a touch input is generated. The touch sensing system executes a touch recognition algorithm and calculates coordinates of the touch data.
The touch sensing system may set its operation mode to an idle mode. When a period, in which there is no touch input, lasts for a predetermined period of time, the touch sensing system operates in the idle mode. The touch sensing system drives the touch screens in a markedly longer cycle than a normal operation mode (or an active mode), so as to reduce power consumption in the idle mode.
As shown in FIG. 1, one period of the idle mode is divided into a sensing time Tsense and an idle time Tidle. The touch sensing system supplies driving signals to the touch sensors through the lines of the touch screen for the sensing time Tsense of the idle mode and senses voltages of the touch sensors. Subsequently, the touch sensing system stops an output of a driving circuit of the touch screen for the idle time Tidle of the idle mode. As a result, the touch sensing system may sense the touch input only within a short sensing time Tsense of each of a first period P(N) and a second period P(N+1) in the idle mode.
The touch sensing system is converted from the idle mode to the normal operation mode when the touch input is sensed in the sensing time Tsense of the idle mode, and shortens a sensing cycle of the touch screen in the normal operation mode. On the other hand, the touch sensing system cannot sense the touch input for the idle time Tidle of the idle mode. When a touch input generated for an idle time Tidle of the first period P(N) lasts up to a sensing time Tsense subsequent to the idle time Tidle, the touch sensing system senses the touch input for the sensing time Tsense of the first period P(N) and is converted from the idle mode to the normal operation mode. Thus, a latency it takes for the touch sensing system to sense the touch input when the idle mode is converted into the normal operation mode may increase by the idle time Tidle. The latency reduces the touch sensitivity the user feels.